This Friday evening, December 22, at just after 8:32pm EST, SpaceX is scheduled to launch the Iridium-4 mission from California’s Vandenberg Air Force Base. The mission will carry a fourth set of 10 Iridium Next satellites into the black aboard a previously-flown Falcon 9 rocket, but at the moment there seems to be more attention being paid to what the mission won’t be doing.

SpaceX confirmed earlier this week that it will not make any attempt to recover the first stage of the Falcon 9 rocket during this mission. The previous Iridium missions all incorporated the landing of the first stage of the Falcon 9 aboard one of SpaceX’s drone-piloted barges, so it is curious that there is no landing attempt planned following this launch.

SpaceX hasn’t offered much in the way of an explanation, but the speculation is that this particular model of the Falcon 9, which is one of the “Block 3” variants, is now considered to be outdated and the company is no longer interested in keeping it in service. SpaceX currently uses a combination of “Block 3” and “Block 4” rockets to carry out its missions, but the company is expected to roll out an updated “Block 5” variant early next year that will be more suitable for reuse. With the “Block 5” rockets joining the fleet, it stands to reason that the “Block 3” models need to make way on the line for their more sophisticated cousins.

Iridium-4 mission patch

Despite the lack of a landing (something that has now become a rarity for a SpaceX launch), the Iridium-4 mission will still be an historic flight. SpaceX will be using the same first stage Falcon 9 rocket for this mission that it used to launch the second set of Iridium satellites back in June of this year. That means this weekend’s launch will mark the first time in history that a company will launch two different sets of satellites in two completely separate missions using the same rocket!

SpaceX’s webcast of Friday’s launch will begin approximately 20 minutes before liftoff at spacex.com and on the company’s YouTube channel. There is an instantaneous launch window, and the backup launch date is December 23.